FM-band transmitters find broad application in many types of wireless devices such as mobile cellular telephones. A typical FM antenna that is integrated in such mobile environments is an electrically small, high Q and highly inefficient antenna. An FM transmitter must be able to generate very large signal swings across the mobile antenna to produce radiated power at the antenna to meet regulatory requirements. These requirements are additionally difficult to satisfy in a mobile device designed to operate around the world, for example across about the 76-108 MHz bands.
Mobile cellular devices may also contain radio receivers on other bands, e.g., Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA) and Global Positioning System (GPS). These other receivers lie at harmonic frequencies of the FM frequency, resulting in interference from the FM transmitter at harmonics of its fundamental frequency. Emissions from the FM transmitter at harmonics of the FM output frequency must therefore be strictly limited, while retaining the ability to linearly generate wide signal swing over a wide band into a high Q inductive antenna.